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Physics simulation Status and plan for 2007

HIP meeting, 20 Mars, 2007. Physics simulation Status and plan for 2007. R. Kinnunen, S. Lehti, L. Wendland Helsinki Institute of Physics. Contents - Analysis of the H ± -> tn , t -> hadrons+ n in fully hadronic channel from gg -> tbH ± for 1 fb -1

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Physics simulation Status and plan for 2007

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  1. HIP meeting, 20 Mars, 2007 Physics simulationStatus and plan for 2007 R. Kinnunen, S. Lehti, L. Wendland Helsinki Institute of Physics R. Kinnunen Helsinki Institute of Physics

  2. Contents • - Analysis of the H± -> tn, t -> hadrons+n in fully hadronic channel from gg -> tbH± for 1 fb-1 • Status of the work and plan for 2007 • - Search for the Higgs bosons in the SUSY cascades with • non-universal boundary conditions at the unification scale • with K. Huitu, J. Laamanen and Tapio Salminen • Other projects: • - t tagging package with impact parameter for CMSSW • by Sami • - Data transfer and computing in Helsinki (Sami) • - H/A->tt-> 2 jets, PhD work by Lauri • - Finalization of CMS note on qqH, H->mm • in collaboration with Chandigarh group, presentation in Physics meeting R. Kinnunen Helsinki Institute of Physics

  3. Analysis of H± -> tn, t -> hadrons+n for1 fb-1 Main results from the full simulation study for PTDR2 CMS NOTE 2006/100 Signal visible as a tiny peak at large transverse masses Extreme phase space corner selected -> large sensitivity to accidendal reconstruction problems R. Kinnunen Helsinki Institute of Physics

  4. Background in the full simulation study Backgrounds from genuine t’s in tt and W+3 jets were found to be well under control: t jet and large ETmiss (> 100 GeV) well measured Background from fake t’s was observed in the signal area mT> 100 GeV: - can originate from fluctuations in jet fragmentation - was found to be mainly due to fake tracks in the signal cone after the tracker isolation The fake t background was efficiently reduced with strong track quality cuts IPT < 0.3 mm and at least 10 hits R. Kinnunen Helsinki Institute of Physics

  5. TOB TOB TIB TIB PXL PXL MC truth Reconstructed Further reduction of QCD-multijet bkg? (Lauri) Signature: - one high pT track - contains hits from different MC tracks - non-zero IP • Problem:- QCD-multijet events contain several tracks in a jet, but sometimes only one is reconstructed  what if the other tracks could be recovered? • Method:- If only one track is reconstructed, redo track fitting from outside in KalmanFilter search window would be smaller and more accurate in pixels higher probability to reconstruct correct pixel hits track pT expected to become softer; some lost tracks expected to be recovered reduction achieved with a pT and n_tracks cut • Application:- both H±->tau nu->(hadr.) and H,A->2tau->(hadr.) Gap between PXL and TIBmost critical region R. Kinnunen Helsinki Institute of Physics

  6. Background measurement from data For measurements of backgrounds with real t’s from W+3 jets and tt backgrounds the precise muon measurement in W->mnand the lepton universality in the W decaycan be exploited Event selection: 1. Events from Single muon trigger 2. Off-line selection: - pTm > 100 GeV - ETmiss > 100 GeV - 3 jets, ET > 20 GeV - no b jets, suppression of tt Simulation: Generate tt and W+3jet events with W->mu R. Kinnunen Helsinki Institute of Physics

  7. The W+3jets, W->tn background can be estimated through: N(W+3jets) = (N(m sel.) – N(tt cont.)) * (et/em) * (1-eb-antitag) / (eb-antitag)3 • et : to be estimated from MC • t’s with large pT could be obtained from W+jet, W->tn but QCD • suppression will be difficult • - eb-antitag : can be measured from g+jet events, if fraction of g+b events • is below 1% • top reconstruction: to be checked if affects the shape of the • mT(t jet, ETmiss)distribution Estimate of the statistics for the muonic selection with the ALPGEN production samples for W+3jet (722 pb) and W+4jets (174 pb): pTm > 100 GeV 16.27 pb MET(from particles) > 100 GeV 1.28 pb 3 jets, ET > 20 GeV 1.05 pb (29% W+4jets) R. Kinnunen Helsinki Institute of Physics

  8. Measurement of tt, W->tn background exploiting muons Event selection for a sample dominated with tt events: - Single muon trigger - pTm > 100 GeV - ETmiss > 100 GeV - 3 jets, ET > 20 GeV - 2 b jets, suppression of W+3jet events The tt, W->tn background can be estimated through: N(tt) = (N(m sel.) – N(W+3jet cont.)) * (et/em) * eb-tag / (eb-tag)2 eb-tag : to be measured in b enriched tt events with the precision of 6% for barrel 10 % for end-caps for 1 fb-1,S. Lowette et al., CMS NOTE 2006/013 R. Kinnunen Helsinki Institute of Physics

  9. Another possibility for tt, W->tn background • A signal free region dominated with tt could be obtained exploiting the • difference in t helicity correlations • Event selection: • single t + MET trigger • ETt-jet > 100 GeV, ETmiss > 100 GeV • 3 jets • 2 b jets, suppression of W+3jets • Rt = pleading track/ Et <~ 0.3 Contributions at low pleadingtrack/Etjet not visible due to trigger selection R. Kinnunen Helsinki Institute of Physics

  10. Suppression of QCD jets: only 1-prong and a cut in Df(t jet, ETmiss) Study of the QCD contribution as a function of Df needed tt events Narrow distribution for QCD jets The tt, W->tn background can be estimated through: N(tt) = (N(observed) – N(W+3jet cont.)) * e(Rt > 0.8)/e(Rt < 0.3)* eb-tab/(eb-tag)2 Suppression of QCD multi-jets with the Df cut may lead to low statistics ! R. Kinnunen Helsinki Institute of Physics

  11. Background from fake t’s originating from fluctuationsin jet fragmentation • Use g + jet events as proposed in CMS NOTE-2006/028 • - 104 events expected for a bin of 0.1xET for 1 fb-1 • apply t identification on the jet • estimate probability for a jet to fake the t as a function of • photon ET R. Kinnunen Helsinki Institute of Physics

  12. Event selection methods and cut optimization for 1 fb-1 • Study of the fake tracks for pTtrack > 80 GeV,need the QCD samples • Particle flow method for t jet energy measurement • Expect improvement in Rt = pleading track/ Et • Work in progress • Include the electron background from W+3jets and tt, W->en, • with electron faking the hadronic t signal, and the bWt background • Re-optimization of jet assignment and top mass reconstruction • Re-optimization of central jet veto for tt suppression: possibly remove, • signal efficiency 35-50% in the PDTR study • Include 3-prong t’s with the new algorithm of D.P. Roy et al. • Monoranjan Guchait (TIFR) joins the project R. Kinnunen Helsinki Institute of Physics

  13. Search for the Higgs bosons in the SUSY events with non-universal boundary conditions at the unification scale with K. Huitu and J. Laamanen and Tapio Salminen • h/A/H-> bb decay channel selected in the SUSY cascades with c02 ->h/A/H c01 • Expect events with many hard jets, large missing ETand 2 b jets from Higgs decay, combinatorial background reduced with a hemisphere separation method • Event generation with PYTHIA and simulation with FAMOS 24-dimensional Representation; H/A can be produced mA = 190 GeV, tanb = 10 Singlet Representation; only h can be produced mA = 190 GeV, tanb = 10 Try to extract the background with fits R. Kinnunen Helsinki Institute of Physics

  14. Back-up slides R. Kinnunen Helsinki Institute of Physics

  15. Production processes Production through two processes: gb -> tH±andgg(qq) -> tbH± gb -> tH± is often considered as the LO process and gg(qq) -> tbH± as a part of the NLO correction to gb -> tH± More energetic b jet from gg(qq) -> tbH± Choise of the production process affects the top mass reconstruction and jet veto Keep the event generation with gg(qq) -> tbH± with the present (LO) generators, gg(qq) -> tbH± can be also considered as the LO process J. Alwal R. Kinnunen Helsinki Institute of Physics

  16. Exploiting helicity correlations in 3-prong t decays The 1-prong t selection with pleadingtrack/Etjet > 0.8 suppresses the 3-prong tdecays from 15% to 3% in the full simulation of the gg -> tbH±, H± -> tnchannel • New idea1) of exploiting more efficiently the 3-prong tdecays • based on the decay mode without any accompanying p0’s: t-> p±p± p± n2/3rd the 3-prong decays (10% of total) This mode can be selected with matching of tracker momentum and calorimeter signals or by a veto on accompanying p0->2g in ECAL • The a1L contribution can be enhanced with a cut in the t momentum • fraction carried by the like-sign pair • R3 < 0.4 or R3 > 0.8, R3 = pp±p±/pt-jet 1) M. Guchait, R. Kinnunen, D.P. Roy, hep-ph/0608324. R. Kinnunen Helsinki Institute of Physics

  17. New selection for 3-prong t decays, hep-ph/0608324 Selection oft->p±p±p±nwith DE = |Etrktot - Ecaltot|<10 GeV ~ calorimeter resolution For R3p < 0.4 the event is triggered at HLT with the 3th opposite sign pion, pT(3th opposite sign p) > 60 GeV for R3p < 0.4 ! R. Kinnunen Helsinki Institute of Physics

  18. Exploiting helicity correlations in 3-prong t decays Study for the gb -> tH±, H± -> tn channel l Event generation with PYTHIA, t decays with TAUOLA l Background from tt events l Fast simulation of CMS detector, jet and missing ET reconstruction l No trigger simulation R3 = pp±p±/pt-jetdistributions for t-> 3p± with ETtjet > 100 GeV R. Kinnunen Helsinki Institute of Physics

  19. Transverse mass reconstruction mT = (2 ETt jet ETmiss (1 - Df(t jet, ETmiss))1/2 Transverse mass distributions for the signal and background with all selection cuts with pTHiggs > 50 GeV • ~1.4 tt events at large mT, with good missing ET measurement and passing track qualitycuts, • are events triggered with a hadronic jet (fake t signal) • can be suppressed requiring strong correlation for the t jet and missing ET • with pTHiggs > 50 GeV (signal efficiencies > 84% ) R. Kinnunen Helsinki Institute of Physics

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